Priority is claimed to Japanese Application No. 2005-072711 filed on Mar. 15, 2005, which is hereby incorporated by reference in its entirety.
1. Technical Field
The present invention relates to a method for manufacturing a semiconductor device and a semiconductor device obtained by the same method.
2. Related Art
Conventionally, there is a method for manufacturing a thin film semiconductor device, such as one represented by a polycrystalline silicon thin film transistor (p-SiTFT), at a temperature no greater than around 600° C. at which a general-purpose glass substrate can be used, or at a temperature no greater than around 425° C. which is about the same temperature at which an amorphous silicon thin film transistor (a-SiTFT) is manufactured.
According to this method, a silicon oxide film, which is an insulation film used as a base protection film, is first deposited on a glass substrate, and an amorphous silicon film that becomes a semiconductor film is then deposited thereon. Then, a XeCl pulse excimer laser (at a wavelength of 308 nm) is irradiated onto this amorphous silicon film to turn it into a polycrystalline silicon film (a laser thermal treatment). In the laser thermal treatment, the temperature of the amorphous silicon film that has absorbed the laser light increases so as to melt the amorphous silicon film, and, when the temperature decreases, the melted silicon film is crystallized to produce the polycrystalline silicon film.
After the laser thermal treatment, the silicon oxide film that becomes a gate insulation film is formed by a chemical vapor deposition method (a CVD method) or a physical vapor deposition method (a PVD method). Then, by forming a gate electrode using tantalum or the like, a metal (gate electrode)—oxide film (gate insulation film)—semiconductor (polycrystalline silicon film) field effect transistor (MOS-FET) is obtained. Finally, after depositing an interlayer insulation film on these films and then opening contact holes, wiring is provided using a metal thin film. As a consequence, a thin film semiconductor device is obtained.
However, with the conventional method for manufacturing the thin film semiconductor device, the energy density changes during the laser thermal treatment because it is difficult to control the energy density of the excimer laser light, and, thus, the quality of the semiconductor film varies largely. Particularly, this variation in the quality of the semiconductor film is notable with the laser irradiation conditions (e.g., radiation energy density) for forming a relatively high-quality polycrystalline semiconductor film. Therefore, in an actual manufacturing process, the energy density is set slightly lower than the optimal density when carrying out the laser irradiation. With the insufficient energy density, however, it is difficult to obtain a high-quality polycrystalline thin film.
Further, even if the laser radiation is carried out at the optimal radiation energy density to produce a relatively high-quality polycrystalline film, the produced silicon film is polycrystalline. A polycrystalline silicon film has a grain boundary at which a leak current occurs, for example, and the properties of the thin film semiconductor device formed thereon are not as good as those of the single-crystalline silicon. Moreover, because it is not possible to control the area where the grain boundary is generated, the properties of the thin film semiconductor device formed on this polycrystalline silicon film largely vary even within the same substrate.
In contrast, there is a known technique (e.g., see JP-A-2003-92260) by which a region having a hole in the center inside the surface of the amorphous silicon film is formed into a silicon film substantially in a single-crystalline state, by first making a hole in an insulation film on a substrate, forming an amorphous silicon film on this insulation film, irradiating this amorphous silicon film with a laser beam under predetermined conditions, and, while maintaining the amorphous silicon at the bottom part of the hole in a non-melting state and bringing the other part of the amorphous silicon film into a melting state, generating crystal growth using the amorphous silicon maintained in the non-melting state as a crystalline nucleus.
However, such a technique for forming the silicon film substantially in the single-crystalline state has some aspects that need to be improved as below.
The single crystal grain (the substantially single-crystalline grain) in the silicon film obtained by this technique has the upper limit (maximum) diameter of about 7 μm at the most. Thus, when forming a transistor in the single crystal grain, the channel cannot be made wide enough. Also, if the channel cannot be made wide enough, the capacity of the transistor cannot be expected to increase, since the amount of current flowing through the channel cannot be increased, for example.